Luminescent molybdate and tungstate compositions



Aug. 29, 1967 L. H. BRIXNER 3,338,841

LUMINESCENT MOLYBDATE AND TUNGSTATE COMPOSITIONS Filed May 14, 1964 4 Sheets-Sheet 1 FIGJ FLUORESCENT EMISSION SPECTRUM OF 5 05 qsWs 4 FIG.4

FLUORESCENT EMISSION SPECTRUM OF 105 N .05 qss ss 4 RELATIVE INTENSITY I I I L I 1 6500 6000 5500 450 475 500 550 600 WAVELENGTH IN ANGSTROHS WAVELENGTH, NILLINICRONS INVENTOR LOTHAR H. BRIXNER ATTORNEY LUMINESCENT MOLYBDATE AND TUNGSTATE COMPOSITIONS Filed May 14. 1964 4 Sheets$heet 2 FIG-2 FLUORESCENT EMISSION SPECTRUM OF (TbNb) (SrW) O INTENSITY l 1 425 450 475 500 550 60 WAVELENGTH IILLIIICRONS INVENTOR LOTHAR H. BRIXN ER ATTORNEY Aug. 29, 1967 L. H. BRIXNER 3,338,841 LUMINESCENT MOLYBDATE AND TUNGSTATE COMPOSITIONS Filed May 14, 1964 4 Sheets-Sheet 3 FLUORESCENT EMISSION SPECTRUM OF mensm WAVELENGTH, NILLIMICR'ONS INVENTOR LOTHAR H. BRIXNER ATTORNEY i RELATIVE INTENSITY 1967 L. H. BRIXNER 3,338,841

LUMINESCENT MOLYBDATE AND TUNGSTATE COMPOSITIONS Filed Ma 14, 1964 4 Sheets-Sheet 4 FLUORESCENT EMISSIOM SPECTRUM. AT 77K OF (NdNb)Q o|(CC|MO)o 99O4 I I Q I m WAVELENGTH, u

INVENTOR LOTHAR H. BRIXNER ATTORNEY United States Patent 3,338,841 LUMINESCENT MOLYBDATE AND TUNGSTATE COMPOSITIONS Lothar H. Brixner, Brandywine Hills, Pa., assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware Filed May 14, 1964, Ser. No. 367,518 Claims. (Cl. 252-30L4) This application is a continuation-in-part of application Ser. No. 286,731, filed June 10, 1963, now abandoned.

This invention relates to new luminescent materials and methods for producing them, and is more particularly directed to novel compositions of matter which are single-phase solid solutions comprising varying proportions of the constituent component oxides XNbO XTaO MWO and MMoO in which X is a trivalent metal selected from the group consisting of rare earth metals of atomic numbers 58 through 60 and 62 through 71, yttrium and scandium, and M is an alkaline earth metal having an atomic number in the range from 20 to 56, inclusive. The invention is further particularly directed to processes for making these compositions by controlled heating of mixtures of oxides of the component metals. More specifically, the novel compositions are single-phase solid solution compounds of the generic formula:

Where A is a trivalent metal selected from the group of rare earth metals of atomic numbers 58 through 60 and 62 through 71, yttrium, and scandium, B is Nb or Ta, C is an alkaline earth metal having an atomic number in the range from 20 to 56, inclusive, i.e. calcium, strontium or barium, D is M0 or W, and O is oxygen, and x is a value of from 0.002 to 0.65; and the novel processes for producing these compositions comprise the steps of (a) intimately mixing in stoichiometric amounts, an oxide of each of the metals of the generic formula; (b) firing the mixture at a temperature of 700 C.-950 C. for a period of from to 14 hours; (c) subjecting the fired product to comminution and remixing; (d) compacting the remixed product; and (e) firing said compacts at a temperature of 1000-l200 C. for 10 to 14 hours.

In the drawings, the fluorescence spectrum for is shown in FIGURE 1, for Tb Nb Sr W O in FIGURE 2, for Sm Nb Sr Mo O in FIGURE 3, for Dy Nb Ba W O in FIGURE 4, and for a single Crystal of Nd 01Nb o1Ca 99MO 9904 in 5, each Of these materials being a composition of the invention.

The new compositions are useful in a multiude of applications because of their outstanding luminescent properties. The novel compositions are particularly valuable as fluorescent phosphors for use at high temperatures in mercury vapor lamps, since the fluorescence of these novel compositions is not quenched at temperatures as high as 325 C. Among other uses are as fluorescent phosphors of difierent colors for lamps, cathodoluminescing compounds for color television, and, in monocrystalline form, as materials for lasers, or optical masers.

The substitution of rare earth ions in crystals of MWO, and MMoO where M is Ca, Sr or Ba, to achieve new and useful optical properties might appear to be logical since the ionic radii of the rare earths are about the same as that of M+ and the rare earth ion fits readily into the tungstate of molybdate lattice in place of a part of the M++ ions. The rare earth ions may be considered, as it were, in solid solution in the MWO or MMoO, crystal. The interaction of electromagnetic radiation with the electronic energy levels of the rare earth ions in this state may be studied and made use of; that is, one may study and make practical use of the absorption of energy by the electrons of the rare earth ion and its re-emission either by fluorescence or in the recently discovered mode of the optical maser, as discussed, for example, in Lasers: Generation of Light by Stimulated Emission by B. A. Lengyel (John Wiley & Sons, New York, 1962).

However, the rare earths are in general tervalent, or their most chemically stable valence is three, and Ca, Sr, and Ba are bivalent. Hence, in substituting a tervalent ion for a bivalent one in a host lattice such as MWO or MMoO extra electrons are added to the lattice. For electrical neutrality of the crystal as a whole, lattice vacancies are created to accommodate the extra electrons; but in general, lattice vacancies occupied by electrons alter the optical properties of the host, complicating the fluorescent emission spectra and raising the threshold energy for initiation of optical maser action (op. cit.), chemical stability is diminished, and, in practice, it is difiicult to grow single crystals having such a defect structure.

To overcome the ditiiculties associated with lattice vacancies, other ions of appropriate radius and valence may be substituted in addition and in amount stoichio metrically equal to the amount of rare earth substituted for the alkaline earth; that is, for example, for each ion of a tervalent rare earth element introduced into the lattice, one may also introduce one univalent ion such as sodium, again into a Ca, Sr, or Ba lattice site, so that electroneutrality of the whole lattice is maintained.

In the present invention it has unexpectedly been found more advantageous to maintain electroneutrality by substituting a quinquevalent ion such as Nb+ or Ta+ into the lattice in place of sexivalent W+ or Mo+ when M+ ions are substituted by, for example, Nd. The chemical stability of this latter type of composition is greater than that of Na+ compensated crystals due to the considerable volatility of alkali metal oxides at the melting temperatures of 15001600 C. used for growing crystals, and further, 'Na+ compensated crystals have some solubility in water. In general, experience with the present invention has shown that monocrystals of better optical, chemical, and even mechanical quality may be grown for optical maser applications by using the Nb+ or Ta+ compensating scheme. A further distinct advantage of this method is that the variation in concentration of rare earth ions along the length of a crystal grown by the well-known Czochralski technique is much less than What has been observed by others using Na compensation.

The foregoing considerations may serve to explain the advantages of charge compensation by introduction of a quinquevalen't ion into a lattice site normally occupied by a sexivalent ion to maintain electroneutrality of the crystal when a tervalent rare earth is substituted for a bivalent alkaline earth ionsuch as Ca++, Sr++, or Ba but are not to be construed as limitations on this invention except as set forth in the appended claims.

It is an object of this invention to produce luminescent compositions of matter which will be useful because of their light emitting ability. These luminescent compositions can be classed in general as band emitters or line emitters and as such find application in a variety of optical instruments. A select group of line-emitters are of particular interest for applications as solid state laser" crystals. The term laser is a well-known acronym for light amplification by stimulated emission of radiation.

Within the scope of the generic formula given above, compositions wherein A, for example, equals yttrium, europium or terbium, have been made and found to have excellent properties over practically the whole region of x from 0.002 to 0.65. For many other compositions of especial interest withinv the generic formula, x 'has been equal to 0.5. The region of x which has been found of particular interest in luminescent, and therefore laser, application is when x is from 0.005 to 0.25. Compositions Within this range and in which A is neodymium and B is niobium have been found to be particularly preferred.

While in the specification and claims of this application reference is made to the use of oxides of specified metals as starting materials, it will be understood that other materials, such as carbonates, which upon heating convert to the desired oxides, are the full equivalent. Similarly, when reference is made to a metal of a specified group, this means at least one such metal and is not to be construed as excluding additional metals of that group.

In the processes of this invention, the component oxides were weighed to the nearest 0.1 milligram according to the stoichiometry desired in the final product, and mixing was effected by ball milling in a mechanical agate ball mill under acetone. In a first firing step, the dried mixture was heated to 700 C. in the case of the molybdenumcontaining compositions, and to 950 for the tungstenconta-ining compositions for to 14 hours. These prereacted products were then homogenized by a second ball milling step, under acetone dried, and pressed to pellets of one inch diameter. In a second firing step, these pellets were fired at 1000-1200 C. for another 10 to 14 hours. The products were subjected to X-ray diffraction analysis, and were found to be completely reacted, homogeneous preparations free of any of the constituent oxides.

The reactants which were used in the preparation of the compounds described herein were of the best commercially available purity, usually 99.9+%. Sc O was prepared by resubliming ScCl which had been obtained by chlorination of thortveitite obtained from Norsk- Feldspat, Norway. The oxides of cerium, praseodymium, and terbium were obtained in a valence state higher than 3. Since it is a requirement of this invention that all of the elements of the rare earth group, or yttrium, or scandium be in the trivalent state, true sesquioxides were prepared by hydrogen reduction of the oxides at 1200 C. To prevent re-oxidation of the compounds thus formed, all of the subsequent reactions in which these three particular oxides were oxides were involved were carried out under ZrTi alloy-gettered argon to prevent possible reoxidation.

Compositions of matter formed according to the general procedure given above were tested for fluorescence under four conditions: At 25 C., under 3660 A. excitation and 2537 A. excitation; and at -196 C. under 3660 A. excitation, and under 2537 A. excitation. In addition to these tests, electrical properties were determined for the compositions and of these, electrical resistivities, dielectric constants, and dissipation factors are reported hereinbelow.

The following examples will preparation of the novel luminescent are the subject of this invention.

illustrate in detail the compositions which Example 1 Compositions of the general formula o.5 o.s o.5 o.s 4

in which A is a trivalent rare earth element or trivalent yttrium or scandium, were prepared by heating together stoichiometric quantities of the component oxides or compounds which upon heating would form these oxides. These oxides were all of at least 99.9% purity. The requisite quantities of the component oxides were carefully weighed to the 0.1 mg., charged to an agate ball mill, and ball milled under acetone for about 60 minutes. The mixture was then removed from the ball mill and dried in air. The homogenized, dried powder mixture was then heated to 950 C. for from 10 to 14 hours. At the conclusion of this heating, the product was again homogenized by a second ball milling under acetone in the agate ball mill for 30 minutes, was again dried and then pressed into a 1 diameter pellet under a pressure of 20,000 to 40,000 p.s.i. The pellets thus formed were subjected to a second firing step at a temperature of 1000 to 1200 C. for 10 to 14 hours. Each product which resulted was a completely reacted homogeneous preparation, whose crystal structure was determined by X-ray diffraction analysis. Structural properties, luminescent properties, and electrical properties of the 13 compositions thus prepared are given in Table 1'. These compositions were prepared according to the above procedure using weights of component oxides, or oxide-forming compounds, as follows:

SERIES NO. 1 [Ao. Nbu.5C8.o.5Wo.5O4]

Weight in Grams Example A-Oxide* NbzOs C210 03 W03 :03 1 .9273 1 .4514 3 .3622 Ytoa 1 .1770 0 .8864 2 .0538 LazOs 0 .8158 0 .6144 1 .4235 StmOa 0 .7619 0 .5738 1 .3296 EuzOa 0 .7552 0 .5687 1 .3173 Gdz03 0 .7347 0 .5533 1 .2817 Tbz03 0 .7266 0 .5471 1 .2675 DyzOs 0 .7128 0 .5368 l .2438 H0203 0 .7034 0 .5297 1 .2275 Error. 0. 6951 0 .5235 0 .2130 T111203 0 .6888 0 .5188 1 .2017 YbzOa 0 .6745 0 .5079 1 .1770 LllzOa 0 .6679 0 .5030 1 .1652

*Wt. in grams of A-Oxide=1.0000 in each case.

Structural, electrical, and luminescent properties of compositions of Series #1 are summarized in Table 1.

TABLE 1 (PART 1) Lattice Parameters Example Composition at, A et, A

Cl).5 0.5 u.5W0.504 structurally Not Identified Yu.a b0.5C o.s o.5O4 5 .202 11 .180 Lau,5Nbu,5C8.o,5W0,5O4 5 .320 11 .455 Smus ot fio .5W0.504 5 .244 11.272 E 0.5 0.5 0.5 0.5O4 5 .234 11.245 Gdo.s bo.5Cau.5W0.504 5 225 11.224 bo.sNbo.aC flj llj i 5 .216 11 .200 DYl).b 0.5 &0.5W0.504 5.208 11 .186 0.5N fl.5 0.5w0.504 5.196 11 .173 Ot Uj flOj UjOA 5 .191 11.161 Tmo.5 bo.5 ao.sW0.504 *5 .24 11 .30 b0.5Nbu.sC9-0.s 0.aO4 "5 .24 *11 .29 Luu.5 bo.5Cau.sWo 504 *5 .25 *11.26

*These three samples also contained a monoclinic fraction with the following parameters:

TABLE 1 (PART 2 Resistivity, Dielectric Dissipation Type of Example ohm-cm. Constant Factor, Emission Percent Band 1 Band.

5.2 X 10 12 9.7 0.9 Do. 6.7 X 10 11.2 1.1 Do. 9.9 X 10 7.9 0.8 Line. 8.3 X 10 8.5 0.9 Do. 7. 6 X 10 11 8. 8 1. 1 Band. 9. 9X 10 11 8.3 0.8 Line. 3.4 X 10 8. 7 0.9 Do. 3.9 X 10 8.1 0.8 Do. 4.7)(10 7.9 0.7 4.9 X 10 9.9 1.3 Band. 5.3 X 10 11 10.1 1.5 Do. 5.7 X 10 10.2 1.6 Do.

1 Band stands for band-emitter, indicating a relatively broad spectrum over a wide spectral range. Line means that these materials are relatively sharp line-emitters, which makes these particular compositions candidates for laser applications, where narrow line width is a prime prerequi- S1 e.

TABLE 1 (PART 3) Fluorescence Color 1 Example Intrinsic Color At 25 0., 3660A., At 25 0., 2537A., At 196 0., At -195 0.,

Excitation Excitation 3660A., Excitation 2537A., Excitation S White S Yellow White. M Yellow White S Greenish White. do W Blue. Do. W Orange W Orange S Orange S Yellow.

S Red S Red S Red. S Yellow White... W Orange S Greenish White. M Greenish W Yellow D0.

Yellow. 1h Light Yellow-.- M Yellow W Bl White S Peach S Bluish White. lj. Peach W Green M Yellow M1 Greenish Yel- OW. 1k Pink M Lemon Yellow. M Yellow White. 11 White W Rose S Yellow White... M Orange S Greenish White. 1m (1 W B1115 M Bluish White. In ...-.do Do.

I The terminology for the identification of visually judged intensities is: S=Strong, M=Medium, W=Weak.

SERIES N O. 2

[A0.5T80.6C30.6W0.504] Exam [6 2 Weight in Grams p Example A-Oxide A second series of novel luminescent compositions Taio Caoo i n -i f in 1a prepared havmg the ge H or u S0203 3.2040 1.4514 3.3622 re 2-32: 2 a .6 5 0.5 0.5 0.5 0.5 4 S11E03 1 .2663 0 .5733 1.329s E11203 1 .2554 0 .5687 1.3174 GdzOa 1.2210 0 .5533 1 .2320 in WhlCh, as in Example 1, A was a metal of the rare gbzga earth group, or scandium, or yttrium, "all in the trivalent j j 1:169) oj5297 2275 state. Using the procedure of Example 1, compositions 23 8-233 were prepared using amounts of the component oxides or YM)3 111210 05079 13770 oxide-forming compounds as given below, the amount of 1111203 1-1104 15029 1-1652 -metal xide bein 1.0000 m. in the each case. A o g g Lummescent and electrical propertles of these compositions were determined and results are recorded in Table 2.

TABLE 2 (PART 1) Emission Resistivity, Dielectric Dissipa- Ex. Composition Type ohm-cm. Constant tion Factor,

TABLE 2 (PART 2) Fluorescence Color Example Intrinsic Color I 25 0., 3660A. 25 0., 25371 0., 3660A., -19e 0., 258711.,

Excitation Excitation Excitation Excitation White M Bluish White--. S Bluish. o .do M Bluish White White Yellow. Light Yellow- White S Bluish White.

s Pink S Yellow White. M B1l)uish White.

o. M Yellow White. W Bluish White.

rin

W Bluish White 'w Red Brown Do dn 7 Example 3 In the same manner as in Examples 1 and 2 above, a series of novel compositions of the generic formula A Nb Ca Mo O were prepared, where A is a metal of the rare earth group, or scandium, or yttrium, each in teh trivalent state. To prepare these compositions stoichiometric amounts of the component oxides were used as follows, the amount of the A-oxide being 1.0000 gm. in each case.

SERIES NO. 3

Electrical and luminescent properties of compositions of Series #3 are summarized in Table 3.

TABLE 3 (PART 1) 8 Example, 4

A fourth series of novel luminescent compositions were prepared having the generic formula SERIES No. 4

[Ao.5 flo.5Ca0.t 0.504]

Weight in Grams Example A-Oxide T2405 C0308 M003 30:03 3 .2040 1 .4514 2 .0874 YzOa 1 .9561 0 .8864 1 .2748 118-203 1 .3558 0 .6144 0 .8836 $111203 1 .2663 0 .5738 0 .8252 E0203 1 .2554 0 .5687 0 .8179 GdzOa 1 .2210 0 .5533 0 .7957 T1320: 1 .2078 0 .5471 0 .7869 Dyzoa 1 .1846 0 .5308 0 .7720 H0203 1 .1690 0 .5297 0 .7619 EH02 1 .1552 0 .5235 0 .7529 T111203 1 .1452 0 .5188 0 .7461 Yb203 1 .1210 0 .5079 0 .7306 1111203 1 .1103 0 .5030 0 .7234

Electrical and luminescent properties of compositions of Series #4 are summarized in Table 4.

TABLE 3 (PART 2) Fluorescence Color Example Intrinsic Color 25 0., 25 C 196 0.,

3660A., 253714., 2537A., Excitation Excitation Excitation 3a. Light Yellow..- S Cream Yellow-- S Yellow. 31 White. W Pink S Light Yellow. 30. do 8 Orange Yellow.

6. Light Tan. S Yellow.

S Orange S Red.

S Orange Yellow. S Greensih Yellow M Pink White.

TABLE 4 (PART 1) Emission Resistivity, Dielectric Dissipation Ex. Composition Type ohm-cm. Constant Factor, Percent 42. S00.5Ta 5M0u.5Ca0,5O4 Band 3.4)(10 8.2 0.9 41) Y Ta0.5Moo.sCao,sO4 do 4.2)( 7.9 0.8 40 L80.5Ta0 5M0o,|5Ca0,rO4 d0 2.3X10 9.4 1.5 4d Smo.sIao.5l\lou 50210504. 4.2Xl0 7.5 1.0 4e Eu0.5Ta0.5M00 5Cao.5O4.. 3.7X10 7.3 0.9 8.8X10 8.2 0.8 4.1)(10 9.3 3.1 5.3X10 8.7 1.2 6.7X10 7.5 1.3 1.3)(l0 7 .2 1.4 8.4)(10 7.9 0.9 7.7)(10 8.2 0.8 6 .4X10 8 .5 1.2

TABLE 4 (PART 2) Fluorescence Color Example Intrinsic Color 0., 3660A., 25 0., 2537A., l96 0., 3660A., 196 0., 2537A., Excitation Excitation Excitation Excitation Light Tan S Cream Yellow S Yellow. White Peach S Lemon Yellow. do W Peach nge S Yellow Orange.

Light Yellow W Red Pink. White S Red S Red S Red.

M Pink M Orange Yellow- S Yellow. S Greenish Yel- S Greenish Yellow. low. M Pink S Pink Yellow.

-do S Pink White. M Yellow Pink W Pink Do. M Pink Do. S Cream Yellow- S Yellow. .do Do.

Example 5 Referring to the information which is given in Tables 1 to 4 above, it will be noted that several of the compositions which are reported showed line emission spectra. These compositions are therefore of particular interest for laser applications. The line emission characteristics are shown in the following study of the particular system Eu Nb Ca W O over a wide range of values for x, these being within the range given above, from 0.002 to 0.65.

Usingthe procedure described in Examples 1 through 4, the following weights (stoichiometric quantities) of oxides were used to prepare compositions of the formulas which are given.

portant potential laser material-s. To use these line emitter materials as lasers, it is, of course, necessary to obtain them in the form of single crystals. To show that the necessary crystals can be formed from the materials of this TABLE 5 Weight of Oxide in Grams Ex. Composition x 1211203 Nbnofl oaoot W0,

EumNbo.utomwmol. 0. 05 1. 0000 0. 7552 10.8052 25. 0303 Eu ,1Nbu.1Cao.0Wo O4 0. l 1. 0000 0. 7552 5. 1182 11. 8565 E110 2Nbn 2Ca0.8W0.sO4 0. 2 1. 0000 0. 7552 2. 2748 5. 2695 E110.26Nb0.25Cao 5Wo.75 4 0. 25 1. 0000 0. 7552 l. 7061 3. 9521 Eu0.55Nbo.s5Ca0.45W0.4504 0. 2. 0000 1. 5104 0. 9306 2. 1558 EliutNbotCatmWMOr 0. 6 2. 0000 1. 6104 0. 7582 1. 7566 Ello.t5Nbo.ttC8.o.3tWo.3504 0. 2. 0000 1. 5104 0. 6124 1. 5188 The purposes in preparing this system of compositions was two-fold: (a) to determine the composition of the material at which the transition from scheelite to fergusonite structure occurs; and (b) to establish the x-value for optimum of fluorescent emission. The scheelite-tofergusonite transition occurs at an x-value of 0.6 to 0.65. The optimum fluorescence emission occurs between x=0.1 and x=0.2. The fluorescence spectrum for the composition of Eu Ca W Nb 0 is given in FIG- URE 1. The spectrographic data on Examples 5a, 5b, 5c, 5d shows clearly that these rare earth compounds are sharp line emitters, and that in the case where the rare earth metal used was europium, the compositions where x=0.l to 0.2 are the most intense in fluorescence.

invention, a single crystal of approximately /2" x 3" was prepared of the material of composition o.04 o.oe oss oes e Chem, 92, 219-221 1917 1 1 Example 6 In the same manner as is described in Example 1, above, additional solid-solution compositions were prepared and luminescent properties were studied. Compositions which were found to be strong line-emitters and therefore preferred compositions were prepared by following the procedure of Example 1 using weights of the constituent oxides (for oxide-forming components) as fol- Compositions 6b and 6l as given in the above table were tested for fluorescence at elevated temperatures. It was found that there was no decrease in the intensity of the fluorescent emission at temperatures at least as high as 325 C.

lows:

TABLE 6 Weights of Component Materials Used in Grams Ex. Composition A NbaOs T2205 CaC 03 W0: MOO:

- Sm.o5Nbo.05Ca0.gsWo.9504 0. 1834 0. 1398 2. 0000 4. 6330 Smo.o5Tau.n5Cao.p5Wn.95O4 0. 1834 0. 2324 2. 0000 4. 6330 Tbn.o5Nbo.o5Cflo.asWo.g5O4 0. 1924 0. 1398 2. 0000 4. 6330 Tbo.u5Tao.o5Cau.95Wu.a5O4 0. 1924 0. 2324 2. 0000 4. 6330 Dyu.05Nbo.n5C80.95Wo.95O4 0. 1962 0. 1398 2. 0000 4. 6330 DyumsTaumgcamswmwo 0. 1962 0. 2324 2. 0000 4. 6330 Sm0.mNb0.oiCau. gM0o.wO4 0. 0352 0. 0268 2. 0000 Smu.o Tan.mC8.u. gM0n.9oO4 0. 0352 0. 0446 2. 000

Tbo.o1Nbo.o oaumMompo 0. 0370 0. 0268 2. 0000 Tbo.n T3.u.mCau.9nM00. p0 0. 0370 0. 0446 2. 0000 Dyo.n Nbo.uiC8o.9 M0o.n9O4 0. 0376 0. 0268 2. 0000 Dyu.oiTB CB mMO t OA 0. 0370 0. 0446 2. 0000 'A= Rare earth metal.

The outstanding luminescent properties of these compositions are shown by the following optical data:

TABLE 7 Most Intense Color of Example 7 Compositions in which the alkaline earth metal, stronat A. tium, was substituted for the calcium of Examples 1 to 6 were made by the procedure of Example 1, using strontium Emu.oagbmsg mawmsgi 5.3% 01 mm. carbonate in place of the calcium carbonate. Products figjj fig-jg l-fi flfg j 2: g; which were strong line-emitters, and therefore preferred n.o5 lllgt)i.ns% uflfivwfi ot $33 g compositions, were obtained using weights of constituent g;g; ,;-;,i; ;3 g3 ,5, 5:720 oxides or oxide-forming components as follows: SmomNbo.mCaumMoomO; 5,700 Orange. S1110 .0i U.0i -0.WM00.9DO4 5, 700 Do. Tbu.o1Nbo.o1C8o.ssM0o.oaO4 5, 420 Green. BM OM BM B.99 4 5, 420 Do. DyomNbmcaosaMon.9 04 5,720 Yellow. Yn.01 o.01C o.aeM o.ea 4 720 D0- TABLE 8 Weights or Component Materials Used in Grams Ex. Composition A103 Nbz05 T8105 SICOa I W03 M00! 73..." Tb,o1Nb mSl,aaW m0; 2. 0000 1400 7b TbmTamSIflaaW 304 2. 0 00 3. 1400 Sm ozNb.nzSr 9sMo.asO4 2.00 0 1 9500 70.. Nd.o Ta.o1Sr wW M04 86. 8625 136. 4478 76...- NdmNbmSLmyW ,9 04 80. 8625 130. 4478 'A=Rare earth metal.

In like manner, products which were strong lineemitters were prepared using barium carbonate in place of the calcium carbonate or strontium carbonate of the prior examples. The compositions, and the proportion of components used to make them, are shown in Table 9.

TABLE 9 Weights of Component Materials Used in Grams Ex- Composition pie A103 NbgOs T8205 BaCO; W03 M00;

7f. Dy o5Nb,o5B8..95W ,9504 0995 0709 2. 0000 2. 3494 7g.. S111 ,mTamBflsgW 904 2. 0000 2. 3494 7h DY.05 b .o5BB..n5M0 .9504 2. 0000 1. 4586 71. Nd.oi b.o1B&.w 0.nsO4 116. 1207 84. 6916 71. Nd n1Nb,n Ba 39W 3904--. 115. 1207 136'. 4478 71L..- Nd .orTB o1Ba q9W,w04 116. 1207 136. 4478 Additional compositions having the same generic formula as 7b, 7c, 7 j, 7g and 7h, above, were prepared, the values for the substitutional amount-s of the rare earth element and of niobium or tantalum being varied from 0.002 to 0.1. These series of compositions were tested to establish the level at which optimum fluorescence was obtained. In each series it was found that the compositions of Examples 7b, 7c, 7]", 7g and 7h exhibited the maximum fluorescence.

FIGURE 2 of the drawings shows the fluorescent emission spectrum for the composition of Example 7a. The composition of Example 7b gave an almost identical emission spectrum. FIGURE 3 shows the fluorescent emission spectrum for the composition of Example 70; the spectrum for 7g was almost identical. FIGURE 4 shows the spectrum for the composition of Example 7 the spectrum for 7h was almost identical.

Examples 8 and 9 To illustrate the properties of the single crystals formed by the compositions of this invention, compositions of he formulas Nd Nb Ca MO 0 (EXample and Nd Nb Sr Mo O (Example 9) Were prepared by charging stoichiometric quantities of Nd O Nb O and CaMo0 (for the first composition), or SrM-oO (for the second composition) into an iridium crucible, melting, and pulling crystals approximately /2" 1:3. For each of these, the strontiurnor calcium molybdate used was prepared in very pure form according to the following procedure:

Solutions of ammonium molybdate and calciumor strontium nitrate (all solutions treated with ammonium and filtered for repurifieation) were reacted to precipitate calcium or strontium molybdate (CaMoO or SrMoO of high purity. The precipitate in each case was filtered, washed and dried at 900 C.

For the preparation of the single crystal of Example 8, 100.00 g. CaMoO 0.8455 g. Nd O and 0.6672 g. Nb O were mixed and melted.

For the preparation of the single crystal of Example 9, 125.00 g. of SrMoO 0.8997 g. Nd O and 0.7103 g. Nb O were mixed and melted.

For the single crystals of Example 8, the laser qualities were tested and the data are given in Table 10.

The fluoroescent emission spectrum for the composition of Example 8 is shown in FIG. 5. The spectrum for composition of Example 9 was essentially identical to this.

To determine at what value of x in the formula Nd Nb Sr Mo 0 the maximum intensity of fluoresence is obtained, a series of compositions were prepared including the composition of Example 9. It was found that for this combination of elements, maximum fluorescence was obtained when x had a value of 0.013.

TABLE 10.-LASER DATA Typical composition -(NdNb) (CaMo). 0 NdNbO Segregation Coefficient in CaMoO -1.3 Lattice Parametersa =5.2l3A., c =11.395A.

Expansion Coefiicient-In a dir.=19.43 10- in c dir.=25.48 X10- Thermal Conductivity-In a dir.=29.5 m watts/cm.-deg.

Refractive Index1.98

Dielectric Const.-In a dir.=12.5 (at 1 kc./sec.)

Melting Point1480 C.

Typical Threshold1.6-l0 joules (195 K.)

Lifetime-420480 sec (295 K.) (150 ,usec at optimum) Line Width5A. (77 K.)

I claim:

1. A single-phase, solid-solution, luminescent composition of the formula Nd Nb Ca Mo O where x has a value between 0.002 and 0.65.

2. A solid-solution, luminescent composition of the formula Nd 013Nb o13cO 9g7MO 9 704, characterized in that, on illumination by electro-magnetic radiation in the ultra-violet region of the spectrum, luminescence occurs by emission of light of a wavelength different from that of the ultra-violet light-emitting source, said luminescence occurring over a very narrow range of spectral wavelength.

3. A single crystal of a single-phase, solid solution luminescent composition of the formula Where x has a value between 0.002 and 0.6.

4. A laser having as the light-emitting and lightamplifying component thereof a single-crystal composition of claim 3.

5. In a method for amplification of light by stimulated emission of radiation the step comprising stimulating by electromagnetic radiation in the ultraviolet region of the spectrum a single crystal composition of claim 4, whereby light is emitted therefrom having wavelengths in a narrow spectral range.

References Cited UNITED STATES PATENTS 3,225,306 12/1965 Johnson et al 252-30l.5 3,257,625 6/1966 Johnson et al. 11 301.4 3,265,628 8/1966 Vogel 252-3015 OTHER REFERENCES Kroger, Some Aspects of the Luminescence of Solids, Elsevier Publishing Co., N.Y., 1948, pgs. 108-1 12, and 290-298.

Kiss et al., Optical Maser Action in CaWO :Er, Proc. IRE, vol. 50, No. 6, June 1962, page 1531.

Nassau, Crystals for Optical Masers, Bell Lab. Record, March 1963, pgs. -99.

TOBIAS E. LEVOW, Primary Examiner. HELEN M. MCCARTHY, Examiner. R. D. EDMONDS, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTHHCAJTIOF CORRECTHNN Patent No. 3,338,841 August 29, 1967 Lothar H. Brixner It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 14, line 18, for "Nd Nb C0 Mo 04" r d Nd ea .0l3 .O13 .987 .987 4 Signed and sealed this 3rd day of September 1968.

(SEAIJ itxtestz EDVDURD.L'BRENNEB.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

1. A SINGLE-PHASE, SOLID-SOLUTION, LUMINESCENT COMPOSITION OF THE FORMULA NDXNBXCA1-XMO1-XO4, WHERE X HAS A VALUE BETWEEN 0.002 AND 0.65. 